Method Of Making Active Materials For Use In Secondary Electrochemical Cells

ABSTRACT

The present invention provides for the preparation of an “optimized” VPO 4  phase or V—P—O/C precursor. The VPO 4  precursor is an amorphous or nanocrystalline powder. The V—P—O/C precursor is amorphous in nature and contains finely divided and dispersed carbon. Throughout the specification it is understood that the VPO 4  precursor and the V—P—O/C precursor materials can be used interchangeably to produce the final vanadium phosphates, with the V—P—O/C precursor material being the preferred precursor. The precursors can subsequently be used to make vanadium based electroactive materials and use of such precursor materials offers significant advantages over other processes known for preparing vanadium phosphate compounds.

This application is a continuation-in-part of U.S. patent applicationSer. No. 11/277,746 filed Mar. 28, 2006, which claims priority from U.S.provisional patent application 60/729,932 filed Oct. 25, 2005, whichclaims priority from U.S. provisional patent application 60/666,132filed Mar. 28, 2005.

FIELD OF THE INVENTION

The present invention relates to the novel preparation of ananocrystalline VPO₄ precursor and in another embodiment to an amorphousV—P—O/C precursor (or V—P—O-carbon composite material/precursor). Theinvention further relates to the use of this VPO₄ precursor or V—P—O/Cprecursor in methods for making vanadium phosphate compounds. Suchmethods for making vanadium phosphates are beneficial in that themethods proceed at faster reaction rates and at lower temperatures thenknown methods for making vanadium phosphates. Such precursors alsoproduce a purer product. The vanadium phosphate compounds so preparedare electroactive and are useful in making electrochemical cells.

BACKGROUND OF THE INVENTION

A battery pack consists of one or more electrochemical cells orbatteries, wherein each cell typically includes a positive electrode, anegative electrode, and an electrolyte or other material forfacilitating movement of ionic charge carriers between the negativeelectrode and positive electrode. As the cell is charged, cationsmigrate from the positive electrode to the electrolyte and,concurrently, from the electrolyte to the negative electrode. Duringdischarge, cations migrate from the negative electrode to theelectrolyte and, concurrently, from the electrolyte to the positiveelectrode.

By way of example and generally speaking, lithium ion batteries areprepared from one or more lithium ion electrochemical cells containingelectrochemically active (electroactive) materials. Such cells typicallyinclude, at least, a negative electrode, a positive electrode, and anelectrolyte for facilitating movement of ionic charge carriers betweenthe negative and positive electrode. As the cell is charged, lithiumions are transferred from the positive electrode to the electrolyte and,concurrently from the electrolyte to the negative electrode. Duringdischarge, the lithium ions are transferred from the negative electrodeto the electrolyte and, concurrently from the electrolyte back to thepositive electrode. Thus with each charge/discharge cycle the lithiumions are transported between the electrodes. Such lithium ion batteriesare called rechargeable lithium ion batteries or rocking chairbatteries.

The electrodes of such batteries generally include an electroactivematerial having a crystal lattice structure or framework from whichions, such as lithium ions, can be extracted and subsequently reinsertedand/or from which ions such as lithium ions can be inserted orintercalated and subsequently extracted. Recently a class of transitionmetal phosphates and mixed metal phosphates have been developed, whichhave such a crystal lattice structure. These transition metal phosphatesare insertion based compounds and allow great flexibility in the designof lithium ion batteries.

A class of such materials is disclosed in U.S. Pat. No. 6,528,033 B1(Barker et al.). The compounds therein are of the general formulaLi_(a)MI_(b)MII_(c)(PO₄)_(d) wherein MI and MII are the same ordifferent. MI is a metal selected from the group consisting of Fe, Co,Ni, Mn, Cu, V, Sn, Cr and mixtures thereof. MII is optionally present,but when present is a metal selected from the group consisting of Mg,Ca, Zn, Sr, Pb, Cd, Sn, Ba, Be and mixtures thereof. More specificexamples of such compounds include compounds wherein MI is vanadium andmore specifically includes Li₃V₂(PO₄)₃. U.S. Pat. No. 6,645,452 B1(Barker et al.) further discloses electroactive vanadium phosphates suchas LiVPO₄F and LiV_(0.9)Al_(0.1)PO₄F.

Although these compounds find use as electrochemically active materialsthese materials are not always economical to produce. Thus it would bebeneficial to have a process for preparing such intercalation materialsat lower temperatures and with faster reaction kinetics. The inventorsof the present invention have now found a method for preparing a novelVPO₄ precursor and a novel V—P—O/C precursor and processes employingsuch precursors to produce vanadium phosphate compounds moreeconomically and efficiently.

SUMMARY OF THE INVENTION

The present invention provides for the preparation of an “optimized”VPO₄ phase or V—P—O/C precursor. The VPO₄ precursor is an amorphous ornanocrystalline powder. The V—P—O/C precursor is amorphous in nature andcontains finely divided and dispersed carbon. Throughout thespecification it is understood that the VPO₄ precursor and the V—P—O/Cprecursor materials can be used interchangeably to produce the finalvanadium phosphates, with the V—P—O/C precursor material being thepreferred precursor. The precursors can subsequently be used to makevanadium based electroactive materials and use of such precursormaterials offers significant advantages over other processes known forpreparing vanadium phosphate compounds.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional diagram illustrating the structureof a non-aqueous electrolyte cylindrical electrochemical cell of thepresent invention.

FIG. 2 is a representative X-ray pattern for a sample of an amorphousV—P—O/C sample prepared at 700° C. for 4 hours as in Example 1.

FIG. 3 is an X-ray powder pattern for a sample of LiVPO₄F for a productprepared according to Example 2.

FIG. 4 is observed, difference and calculated plot obtained fromRietveld analysis of an optimized sample of LiVPO₄F prepared in Example2.

FIG. 5 shows a schematic representation of the structure of LiVPO₄Fprojected down the c-axis.

FIG. 6 shows the first cycle current data for a Li//LiVPO₄F cell madewith the LiVPO₄F prepared in Example 2.

FIG. 7 shows a representative X-ray powder patterns forLiV_(1−x)Al_(x)PO₄F made by the process according to Example 3.

FIG. 8 shows the unit cell volume versus Al content forLiV_(1−x)Al_(x)PO₄F made by the process according to Example 3.

FIG. 9 shows a comparison of the electrochemical response ofLi//LiVPO₄F, Li//LiAl_(0.25)V_(0.75)PO₄F and Li//LiAl_(0.5)V_(0.5)PO₄Fcells made by the process of Example 3.

FIG. 10 shows a representative X-ray powder pattern for LiVP₂O₇ made bythe process of Example 5.

FIG. 11 shows the observed, difference and calculated plots obtained fora sample of LiVP₂O₇ made by the process of Example 5.

FIG. 12 shows a schematic representation of the structure of LiVP₂O₇made by the process of Example 5.

FIG. 13 shows a first cycle constant current data for a Li//LiVP₂O₇cell.

FIG. 14 shows EVS data for a representative Li//LiVP₂O₇ cell cycledbetween 2.5-4.7 V. Left: EVS Voltage profile. Right: EVS DifferentialCapacity Profile.

FIG. 15 shows EVS data for a representative graphite//LiVP₂O₇ lithiumion cell cycled between 2.5-4.6 V. The data shown is for the tenthcycle. Left: EVS Voltage Profile. Right EVS Differential CapacityProfile.

FIG. 16 shows the life cycle data collected for LiVP₂O₇//graphite cell.

FIG. 17 shows X-ray patterns for samples of LiV_(1−x)Al_(x)PO₄F preparedaccording to the process of Example 10.

FIG. 18 shows the electrochemical results for samples ofLiV_(1−x)Al_(x)P₂O₇ prepared according to Example 10.

FIG. 19 shows a comparison of a sample of LVP prepared usingconventional known methods and prepared using the VPO₄ process accordingto Example 11.

FIG. 20 shows the EVS electrochemical response for LVP sample preparedaccording to Example 11

FIG. 21 shows the X-ray powder pattern for the sample of Na₃V₂(PO₄)₂F₃prepared according to the method of Example 12.

DETAILED DESCRIPTION OF THE INVENTION

Specific benefits and embodiments of the present invention are apparentfrom the detailed description set forth herein below. It should beunderstood, however, that the detailed description and specificexamples, while indicating embodiments among those preferred, areintended for purposes of illustration only and are not intended to limitthe scope of the invention.

The following is a list of some of the definitions of various terms usedherein:

As used herein “battery” refers to a device comprising one or moreelectrochemical cells for the production of electricity. Eachelectrochemical cell comprises an anode, a cathode and an electrolyte.

As used herein the terms “anode” and “cathode” refer to the electrodesat which oxidation and reduction occur, respectively, during batterydischarge. During charging of the battery, the sites of oxidation andreduction are reversed.

As used herein the terms “nominal formula” or “nominal general formula”refer to the fact that the relative proportion of atomic species mayvary slightly on the order of 2 percent to 5 percent, or more typically,1 percent to 3 percent.

As used herein the words “preferred” and “preferably” refer toembodiments of the invention that afford certain benefits under certaincircumstances. Further the recitation of one or more preferredembodiments are not useful and is not intended to exclude otherembodiments from the scope of the invention.

Referring to FIG. 1, a secondary electrochemical cell 10 having anelectrode active material described herein below as nominal generalformula (I), is illustrated. The cell 10 includes a spirally coiled orwound electrode assembly 12 enclosed in a sealed container, preferably arigid cylindrical casing 14. The electrode assembly 12 includes: apositive electrode 16 consisting of, among other things, an electrodeactive material described herein below; a counter negative electrode 18;and a separator 20 interposed between the first and second electrodes16, 18. The separator 20 is preferably an electrically insulating,ionically conductive microporous film, and composed of a polymericmaterial selected from the group consisting of polyethylene,polyethylene oxide, polyacrylonitrile and polyvinylidene fluoride,polymethyl methacrylate, polysiloxane, copolymers thereof, andadmixtures thereof.

Each electrode 16, 18 includes a current collector 22 and 24,respectively, for providing electrical communication between theelectrodes 16, 18 and an external load. Each current collector 22, 24 isa foil or grid of an electrically conductive metal such as iron, copper,aluminum, titanium, nickel, stainless steel, or the like, having athickness of between 5 μm and 100 μm, preferably 5 μm and 20 μm.Optionally, the current collector may be treated with an oxide-removingagent such as a mild acid and the like, and coated with an electricallyconductive coating for inhibiting the formation of electricallyinsulating oxides on the surface of the current collector 22, 24.Examples of suitable coatings include polymeric materials comprising ahomogenously dispersed electrically conductive material (e.g. carbon),such polymeric materials including: acrylics including acrylic acid andmethacrylic acids and esters, including poly (ethylene-co-acrylic acid);vinylic materials including poly(vinyl acetate) and poly(vinylidenefluoride-co-hexafluoropropylene); polyesters including poly(adipicacid-co-ethylene glycol); polyurethanes; fluoroelastomers; and mixturesthereof.

The positive electrode 16 further includes a positive electrode film 26formed on at least one side of the positive electrode current collector22, preferably both sides of the positive electrode current collector22, each film 26 having a thickness of between 10 μm and 150 μm,preferably between 25 μm an 125 μm, in order to realize the optimalcapacity for the cell 10. The positive electrode film 26 is preferablycomposed of between 80% and 99% by weight of an electrode activematerial described herein below as general formula (I), between 1% and10% by weight binder, and between 1% and 10% by weight electricallyconductive agent.

Suitable binders include: polyacrylic acid; carboxymethylcellulose;diacetylcellulose; hydroxypropylcellulose; polyethylene; polypropylene;ethylene-propylene-diene copolymer; polytetrafluoroethylene;polyvinylidene fluoride; styrene-butadiene rubber;tetrafluoroethylene-hexafluoropropylene copolymer; polyvinyl alcohol;polyvinyl chloride; polyvinyl pyrrolidone;tetrafluoroethylene-perfluoroalkylvinyl ether copolymer; vinylidenefluoride-hexafluoropropylene copolymer; vinylidenefluoride-chlorotrifluoroethylene copolymer; ethylenetetrafluoroethylenecopolymer; polychlorotrifluoroethylene; vinylidenefluoride-pentafluoropropylene copolymer; propylene-tetrafluoroethylenecopolymer; ethylene-chlorotrifluoroethylene copolymer; vinylidenefluoride-hexafluoropropylene-tetrafluoroethylene copolymer; vinylidenefluoride-perfluoromethylvinyl ether-tetrafluoroethylene copolymer;ethylene-acrylic acid copolymer; ethylene-methacrylic acid copolymer;ethylene-methyl acrylate copolymer; ethylene-methyl methacrylatecopolymer; styrene-butadiene rubber; fluorinated rubber; polybutadiene;and admixtures thereof. Of these materials, most preferred arepolyvinylidene fluoride and polytetrafluoroethylene.

Suitable electrically conductive agents include: natural graphite (e.g.flaky graphite, and the like); manufactured graphite; carbon blacks suchas acetylene black, Ketzen black, channel black, furnace black, lampblack, thermal black, and the like; conductive fibers such as carbonfibers and metallic fibers; metal powders such as carbon fluoride,copper, nickel, and the like; and organic conductive materials such aspolyphenylene derivatives.

The negative electrode 18 is formed of a negative electrode film 28formed on at least one side of the negative electrode current collector24, preferably both sides of the negative electrode current collector24. The negative electrode film 28 is composed of between 80% and 95% ofan intercalation material, between 2% and 10% by weight binder, and(optionally) between 1% and 10% by weight of an electrically conductiveagent.

Intercalation materials suitable herein include: transition metaloxides, metal chalcogenides, carbons (e.g. graphite), and mixturesthereof capable of intercalating the alkali metal-ions present in theelectrolyte in the electrochemical cell's nascent state.

In one embodiment, the intercalation material is selected from the groupconsisting of crystalline graphite and amorphous graphite, and mixturesthereof, each such graphite having one or more of the followingproperties: a lattice interplane (002) d-value (d₍₀₀₂₎) obtained byX-ray diffraction of between 3.35 Å to 3.34 Å, inclusive (3.35Å≦d₍₀₀₂₎≦3.34 Å), preferably 3.354 Å to 3.370 Å, inclusive (3.354Å≦d₍₀₀₂₎≦3.370 Å; a crystallite size (L_(c)) in the c-axis directionobtained by X-ray diffraction of at least 200 Å, inclusive (L_(c)≧200Å), preferably between 200 Å and 1,000 Å, inclusive (200 Å≦L_(c)≦1,000Å); an average particle diameter (P_(d)) of between 1 μm to 30 μm,inclusive (1 μm ≦P_(d)≦30 μm); a specific surface (SA) area of between0.5 m²/g to 50 m²/g, inclusive (0.5 m²/g≦SA≦50 m²/g); and a true density(ρ) of between 1.9 g/cm³ to 2.25 g/cm³, inclusive (1.9 g/cm³≦ρ≦2.25g/cm³).

Referring again to FIG. 1, to ensure that the electrodes 16, 18 do notcome into electrical contact with one another, in the event theelectrodes 16, 18 become offset during the winding operation duringmanufacture, the separator 20 “overhangs” or extends a width “a” beyondeach edge of the negative electrode 18. In one embodiment, 50 μm≦a≦2,000μm. To ensure alkali metal does not plate on the edges of the negativeelectrode 18 during charging, the negative electrode 18 “overhangs” orextends a width “b” beyond each edge of the positive electrode 16. Inone embodiment, 50 μm≦b≦2,000 μm.

The cylindrical casing 14 includes a cylindrical body member 30 having aclosed end 32 in electrical communication with the negative electrode 18via a negative electrode lead 34, and an open end defined by crimpededge 36. In operation, the cylindrical body member 30, and moreparticularly the closed end 32, is electrically conductive and provideselectrical communication between the negative electrode 18 and anexternal load (not illustrated). An insulating member 38 is interposedbetween the spirally coiled or wound electrode assembly 12 and theclosed end 32.

A positive terminal subassembly 40 in electrical communication with thepositive electrode 16 via a positive electrode lead 42 provideselectrical communication between the positive electrode 16 and theexternal load (not illustrated). Preferably, the positive terminalsubassembly 40 is adapted to sever electrical communication between thepositive electrode 16 and an external load/charging device in the eventof an overcharge condition (e.g. by way of positive temperaturecoefficient (PTC) element), elevated temperature and/or in the event ofexcess gas generation within the cylindrical casing 14. Suitablepositive terminal assemblies 40 are disclosed in U.S. Pat. No. 6,632,572to Iwaizono, et al., issued Oct. 14, 2003; and U.S. Pat. No. 6,667,132to Okochi, et al., issued Dec. 23, 2003. A gasket member 42 sealinglyengages the upper portion of the cylindrical body member 30 to thepositive terminal subassembly 40.

A non-aqueous electrolyte (not shown) is provided for transferring ioniccharge carriers between the positive electrode 16 and the negativeelectrode 18 during charge and discharge of the electrochemical cell 10.The electrolyte includes a non-aqueous solvent and an alkali metal saltdissolved therein capable of forming a stable SEI layer on the negativeelectrode (most preferably, a lithium salt). In the electrochemicalcell's nascent state (namely, before the cell undergoes cycling), thenon-aqueous electrolyte contains one or more metal-ion charge carriers.

Suitable solvents include: a cyclic carbonate such as ethylenecarbonate, propylene carbonate, butylene carbonate or vinylenecarbonate; a non-cyclic carbonate such as dimethyl carbonate, diethylcarbonate, ethyl methyl carbonate or dipropyl carbonate; an aliphaticcarboxylic acid ester such as methyl formate, methyl acetate, methylpropionate or ethyl propionate; a .gamma.-lactone such asγ-butyrolactone; a non-cyclic ether such as 1,2-dimethoxyethane,1,2-diethoxyethane or ethoxymethoxyethane; a cyclic ether such astetrahydrofuran or 2-methyltetrahydrofuran; an organic aprotic solventsuch as dimethylsulfoxide, 1,3-dioxolane, formamide, acetamide,dimethylformamide, dioxolane, acetonitrile, propylnitrile, nitromethane,ethyl monoglyme, phospheric acid triester, trimethoxymethane, adioxolane derivative, sulfolane, methylsulfolane,1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone a propylenecarbonate derivative, a tetrahydrofuran derivative, ethyl ether,1,3-propanesultone, anisole, dimethylsulfoxide and N-methylpyrrolidone;and mixtures thereof. A mixture of a cyclic carbonate and a non-cycliccarbonate or a mixture of a cyclic carbonate, a non-cyclic carbonate andan aliphatic carboxylic acid ester, are preferred.

Suitable alkali metal salts, particularly lithium salts, include:LiClO₄; LiBF₄; LiPF₆; LiAlCl₄; LiSbF₆; LiSCN; LiCF₃SO₃; LiCF₃CO₂;Li(CF₃SO₂)₂; LiAsF₆; LiN(CF₃SO2)₂; LiB₁₀Cl₁₀; a lithium lower aliphaticcarboxylate; LiCl; LiBr; Lil; a chloroboran of lithium; lithiumtetraphenylborate; lithium imides; LiBOB (lithium bis(oxalate)borate)and mixtures thereof. Preferably, the electrolyte contains at leastLiPF₆.

One embodiment of the invention involves the production of ananocrystalline and/or amorphous VPO₄. This material can be used aprecursor for preparing various vanadium based products. This materialis very reactive and allows for the preparation of various vanadiumbased products at low temperatures and with very fast kinetics.Additionally this VPO₄ is useful as a precursor of vanadium basedproducts in that other processes for making the vanadium based productsmay cause production of unwanted impurity phases, such as V₂O₃, in thevanadium based products.

In another embodiment the invention involves the production of aamorphous V—P—O/C precursor with no “definite” composition (see FIG. 2).This V—P—O/C precursor has the correct ratio of V and PO₄ to make thefinal product (e.g. LiVPO₄F), is close to X-ray amorphous (see FIG. 2)and it contains finely divided and dispersed carbon. This material canbe used a precursor for preparing various vanadium based products Thismaterial is very reactive and allows for the preparation of variousvanadium based products at low temperatures and with very fast kinetics.Additionally this V—P—O/C precursor is useful as a precursor of vanadiumbased products in that other processes for making the vanadium basedproducts may cause production of unwanted impurity phases, such as V₂O₃,in the vanadium based products.

It is understood that the VPO₄ and V—P—O/C precursor materials can beused interchangeably in the reactions described herein. The V—P—O/Cprecursor is the preferred precursor. Thus where it is stated that VPO₄is used the V—P—O/C precursor could alternately be used and vice versa.Alternatively, either precursor may be referred to as a vanadiumphosphate precursor.

The vanadium phosphate precursor is made for example by mixing vanadiumpentoxide (V₂O₅), ammonium hydrogen phosphate [(NH₄)₂HPO₄ or (NH₄)H₂PO₄]and a source of carbon, such as Enasco carbon. The mixture is thenmilled and/or micronized (i.e. some form of high energymixing/homogenizing), pelletized and heated at a temperature in therange from about 400° C. to about 900° C. Preferably the milled mixtureis heated in the temperature range from about 500° C. to about 800° C.and more preferably from about 600° C. to about 750° C. The mixture isheated from about 30 minutes to about 16 hours and more preferably fromabout 1 to about 8 hours.

The amorphous V—P—O/C precursors may be produced at temperatures from300-800° C. and more preferably at about 600° C. Reaction of thesepreferred amorphous V—P—O/C precursors with appropriate alkali metalcompounds result in improved vanadium phosphate products which can beproduced at lower temperatures than when using the crystalline VPO₄precursors.

The reaction proceeds according to the following equations:0.5 V₂O₅+(NH₄)₂HPO₄+carbon→VPO₄+2NH₃+1.5 H₂O+COor0.5 V₂O₅+(NH₄)H₂PO₄+carbon→VPO₄+NH₃+1.5 H₂O.

Alternatively other vanadium containing compounds such as V₂O₃, VO₂,NH₄VO₃ and the like can be used in the place of the V₂O₅. If lithiumproducts are the desired end products LiVO₃ and the like may also beemployed in place of the V₂O₃. Likewise, alternatively other phosphatesources such as P₂O₅, H₃PO₄ and the like can be used in place of theammonium phosphate starting materials.

In one aspect, the source of carbon is provided by elemental carbon,preferably in particulate form such as graphites, amorphous carbon,carbon blacks and the like. In another aspect, the source of carbon mayalso be provided by an organic precursor material, or by a mixture ofelemental carbon and organic precursor material. The organic precursormaterial will also be referred to in this application as an organicmaterial. The organic material or organic precursor material is one thatis capable of forming a decomposition product that contains carbon. Thecarbon is formed in situ.

Alternatively or in addition, the source of carbon may be provided by anorganic material. The organic material is characterized as containingcarbon and at least one other element, preferably hydrogen. The organicmaterial generally forms a decomposition product, referred to herein asa carbonaceous material, upon heating under the conditions of thereaction.

The organic precursor material may be any organic material capable ofundergoing pyrolysis or carbonization, or any other decompositionprocess that leads to a carbonaceous material rich in carbon. Suchprecursors include in general any organic material, i.e., compoundscharacterized by containing carbon and at least one other element.Although the organic material may be a perhalo compound containingessentially no carbon-hydrogen bonds, typically the organic materialscontain carbon and hydrogen. Other elements, such as without limitation,halogens, oxygen, nitrogen, phosphorus, and sulfur, may be present inthe organic material, as long as they do not significantly interferewith the decomposition process. One example of a preferred organicmaterial is coke, which contains mostly carbon and hydrogen. Otherprecursors include, without limitation, organic hydrocarbons, alcohols,esters, ketones, aldehydes, carboxylic acids, sulfonates, and ethers.Preferred precursors include the above species containing aromaticrings, especially the aromatic hydrocarbons such as tars, pitches, andother petroleum products or fractions. As used here, hydrocarbon refersto an organic compound made up of carbon and hydrogen, and containing nosignificant amounts of other elements. Hydrocarbons may containimpurities having some heteroatoms. Such impurities might result, forexample, from partial oxidation of a hydrocarbon or incompleteseparation of a hydrocarbon from a reaction mixture or natural sourcesuch as petroleum.

Other organic precursor materials include sugars and othercarbohydrates, including derivatives and polymers. Examples of polymersinclude, without limitation, starch, cellulose, and their ether or esterderivatives. Other derivatives include, without limitation, thepartially reduced and partially oxidized carbohydrates discussed below.On heating, carbohydrates readily decompose to form carbon and water.The term carbohydrates as used here encompasses the D-, L-, andDL-forms, as well as mixtures, and includes material from natural orsynthetic sources.

In one sense as used in the invention, carbohydrates are organicmaterials that can be written with molecular formula (C)_(m) (H₂O)_(n),where m and n are integers. For simple hexose or pentose sugars, m and nare equal to each other. Non-limiting examples of hexoses of formulaC₆H₁₂O₆ include allose, altose, glucose, mannose, gulose, inose,galactose, talose, sorbose, tagatose, and fructose. Pentoses of formulaC₅H₁₀O₅ are represented by, without limitation, ribose, arabinose, andxylose. Tetroses include erythrose and threose, while glyceric aldehydeis a triose. Other carbohydrates include the two-ring sugars(di-saccharides) of general formula C₁₂H₂₂O₁₁. Examples include, withoutlimitation, sucrose, maltose, lactose, trehalose, gentiobiose,cellobiose, and melibiose. Three-ring (trisaccharides such as raffinose)and higher oligomeric and polymer carbohydrates may also be used.Non-limiting examples include starch and cellulose. As noted above, thecarbohydrates readily decompose to carbon and water when heated to asufficiently high temperature. The water of decomposition tends to turnto steam under the reaction conditions and volatilize.

It will be appreciated that other materials will also tend to readilydecompose to H₂O and a material very rich in carbon. Such materials arealso intended to be included in the term “carbohydrate” as used in theinvention. Such materials include slightly reduced carbohydrates suchas, without limitation, glycerol, sorbitol, mannitol, iditol, dulcitol,talitol, arabitol, xylitol, and adonitol, as well as “slightly oxidized”carbohydrates such as, without limitation, gluconic, mannonic,glucuronic, galacturonic, mannuronic, saccharic, manosaccharic,ido-saccharic, mucic, talo-mucic, and allo-mucic acids. The formula ofthe slightly oxidized and the slightly reduced carbohydrates is similarto that of the carbohydrates.

A preferred carbohydrate is sucrose. Under the reaction conditions,sucrose melts at about 150-180° C. The liquid melt tends to distributeitself among the starting materials. At temperatures above about 450°C., sucrose and other carbohydrates decompose to form carbon and water.The as-decomposed carbon powder is in the form of fresh amorphous fineparticles with high surface area and high reactivity.

The organic precursor material may also be an organic polymer. Organicpolymers include without limitation, polyolefins such as polyethyleneand polypropylene, butadiene polymers, isoprene polymers, vinyl alcoholpolymers, furfuryl alcohol polymers, styrene polymers includingpolystyrene, polystyrene-polybutadiene and the like, divinylbenzenepolymers, naphthalene polymers, phenol condensation products includingthose obtained by reaction with aldehyde, polyacrylonitrile, polyvinylacetate, as well as cellulose starch and esters and ethers thereofdescribed above.

In some embodiments, the organic precursor material is a solid availablein particulate form. Particulate materials may be combined with theother particulate starting materials and reacted by heating according tothe methods described above.

In other embodiments, the organic precursor material may be a liquid. Insuch cases, the liquid precursor material is combined with the otherparticulate starting materials to form a mixture. The mixture is heated,whereupon the organic material forms a carbonaceous material in situ.The liquid precursor materials may also advantageously serve or functionas a binder in the starting material mixture as noted above.

In an alternative embodiment of the invention the vanadium phosphateprecursor is made for example by mixing vanadium pentoxide (V₂O₅),ammonium hydrogen phosphate [(NH₄)₂HPO₄ or (NH₄)H₂PO₄]. The mixture isthen milled and/or micronized (i.e. some form of high energymixing/homogenizing), pelletized and heated at a temperature in therange from about 400° C. to about 900° C. in the presence of reducinggas or gases. Non-limiting examples or reducing gases include hydrogen,methane, ammonia and carbon monoxide. The reducing atmosphere may beprovided as pure reducing gas, or as mixtures of reducing gas with othergases. Non-limiting examples of reducing atmosphere mixtures includehydrogen-argon, hydrogen-nitrogen, carbon monoxide-hydrogen, carbonmonoxide-argon, and the like. The reducing gas may but need not beprovided in molar excess. The reducing gas may be used in partialpressures from about 0.01 atmosphere up to super-atmospheric, dependingon such factors as the size of the sample, the volume of the heatingchamber, and the excess of gas, if any, required for the reaction

In an alternate embodiment the reaction is carried out in a reducingatmosphere in the presence of a reductant. Such reductant includes,without limitation carbon and organic precursor materials as discussedabove. Such reducing atmosphere, includes without limitation, thereducing gases and mixtures thereof discussed above.

In one embodiment of the invention the vanadium phosphate precursor ismixed with an alkali metal containing compound and optionally withanother metal containing compound to produce alkali metal vanadiumphosphate compounds. By way of example alkali metal containing compoundsinclude NaF, LiF, LiH₂PO₄, NaOH, Na₂CO₃, Li₃PO₄ and the like andmixtures thereof. If the desired end product is a fluorophosphate (e.g.NaVPO₄F, LiVPO₄F) suitable precursors can include NH₄F and the liketogether with an appropriate alkali ion salt. Preferred alkali metalcontaining compounds are compounds containing Na or Li and the morepreferred alkali metal containing compounds contain Li. The optionalmetal containing compounds are compounds containing a metal ion selectedfrom the group consisting of Al, Ti, Cr, Fe Mn, Mo, Nb and the like.Examples of such metal containing compounds include for example AlPO₄,Fe₂O₃, Mn₂O₃, Fe₃O₄, FeO, MnO₂, MnO, CrPO₄, FePO₄ MnPO₄, aluminumhydroxide, aluminum oxide, aluminum carbonate, Cr₂O₃, Nb₂O₅ and thelike.

The vanadium phosphate precursors are then reacted with an appropriatealkali metal according to, for example the following reactions:3 LiH₂PO₄+2 VPO₄→Li₃V₂(PO₄)₃+3H₂OorVPO₄+LiF→LiVPO₄For3 NaF+2 VPO₄→Na₃V₂(PO₄)₂F₃.

The alkali metal compound is a compound of lithium, sodium, orpotassium. The alkali metal compound serves as a source of alkali metalion in particulate form. Preferred alkali metal compounds are sodiumcompounds and lithium compounds. Examples of compounds include, withoutlimitation, carbonates, metal oxides, hydroxides, sulfates, aluminates,phosphates and silicates. Examples of lithium compounds thus include,without limitation, lithium carbonates, lithium metal oxides, lithiummixed metal oxides, lithium hydroxides, lithium aluminates, and lithiumsilicates, while analogous sodium compounds are also preferred. Apreferred lithium compound is lithium carbonate. Sodium carbonate andsodium hydroxide are preferred sodium compounds.

Typically the VPO₄ precursor, alkali metal containing compound andoptional other metal containing compound are milled and then pelletized.The mixture is then heated at a temperature from about 500° C. to about900° C. More preferably the mixture is heated from about 500° C. toabout 800° C. and most preferably from about 600° C. to about 750° C.The mixture is heated for about 30 minutes to about 16 hours and morepreferably from about 1 to about 8 hours.

The reaction produces electrode active compounds represented by thenominal general formula (I):A_(a)V_(1−x)M_(x)(PO₄)_(d)Z_(f).  (I)wherein A is selected from the group consisting of Li, Na, K andmixtures thereof;

-   a is greater than 0.1 and less than or equal to 3;-   x is zero or less than 1;-   d is greater than 0 and less than or equal to 3-   M is a metal selected from the group consisting of Al, Ti, Cr, Fe,    Mn, Mo, Nb and mixtures thereof;-   Z is F, Cl, or OH:-   and f is greater than or equal to 0 but less than or equal to 3.

Examples of such compounds include but are not limited to LiVPO₄,LiV_(1−x)Al_(x)PO₄F, Na_(x)VPO₄F_(x), Li_(0.1)Na_(0.9)VPO₄F, NaVPO₄F,NaVPO₄OH, NaVPO₄F, Li₃V₂(PO₄)₃, LiV_(0.75)Al_(0.25)PO₄F,LiV_(0.5)Al_(0.5)PO₄F, Na_(1.2)VPO₄F_(1.2) and Na₃V₂(PO₄)₂F₃, and thelike.

In another embodiment of the invention the reaction produces electrodeactive compounds represented by the nominal general formula (I):A_(a)V_(1−x)M_(x)P₂O₇  (I)

-   wherein A is selected from the group consisting of Li, Na, K and    mixtures thereof;-   a is greater than 0.1 and less than or equal to 3;-   x is greater than or equal 0 and less than 1; and-   M is a metal selected from the group consisting of Al, Ti, Cr, Cr,    Fe, Mn, Mo, Nb and mixtures thereof. An example of such electrode    active material includes, but is not limited to LiVP₂O₇.

The electrode active materials described herein are in their nascent oras-synthesized state, prior to undergoing cycling in an electrochemicalcell. The components of the electrode active material are selected so asto maintain electroneutrality of the electrode active material. Thestoichiometric values of one or more elements of the composition maytake on non-integer values.

In all embodiments described herein, moiety Z (when provided) isselected from the group consisting of OH (hydroxyl), a halogen, ormixtures thereof. In one embodiment, Z is selected from the groupconsisting of OH, F (Fluorine), Cl (Chlorine), and mixtures thereof. Inanother embodiment, Z is OH. In another embodiment, Z is F, or a mixtureof F with OH or Cl.

Typically for electrochemical testing, composite electrodes werefabricated using 84-wt % active material, 6-wt % Super P (conductivecarbon) and 10-wt % PVdf-HFP co-polymer (Elf Atochem) binder. Theelectrolyte comprised a 1 M LiPF₆ solution in ethylenecarbonate/dimethyl carbonate (2:1 by weight) while a dried glass fiberfilter (Whatman, Grade GF/A) was used as the electrode separator. Acommercially available crystalline graphite or lithium metal foil wereused as the anode active material. High-resolution electrochemicalmeasurements were performed using the Electrochemical VoltageSpectroscopy (EVS) technique. (J. Barker, Electrochim. Acta, 40, 1603(1995)). EVS is a voltage step method, which provides a high resolutionapproximation to the open circuit voltage curve for the electrochemicalsystem under investigation. Cycling tests of the hybrid-ion cells wereperformed using a commercial battery cycler (Maccor Inc., Tulsa, Okla.,USA).

The following non-limiting examples illustrate the compositions andmethods of the present invention.

EXAMPLE 1 Preparation of VPO₄

VPO₄ was prepared according to the following reaction:½ V₂O₅+(NH₄)₂HPO₄+1.0 C→VPO₄+2 NH₃+3/2 H₂O+CO9.1 g V₂O₅, 13.2 g of (NH₄)₂HPO₄ and 1.32 g of carbon (10% mass excess)were used. Carbon was added to the reaction mixture so that the V⁵⁺ inthe V₂O₅ was reduced to V³⁺ in the product which is an example ofcarbothermal reduction. The excess carbon in the product helps act as aconducting agent in the vanadium phosphate electroactive materialsproduced therefrom, which improves the electrochemical properties ofsuch electroactive materials.

It has been found that it is necessary to use a homogenous startingmaterial. This can be achieved using high energy milling methods, whichcan include ball milling and micronizing. The sample prepared hereinwere prepared using McCrone micronizers to obtain the startingmaterials.

The VPO₄ materials prepared herein were prepared at a number ofdifferent temperatures in the range from about 650° C. to about 900° C.The samples prepared at higher temperatures contained V₂O₃ as animpurity. Such materials would be unsuitable as precursors since V₂O₃ isknown to be detrimental to the electrochemical performance in Li ioncells. It has been found that preparing these materials at lowtemperatures, typically about 700° C. for about 4 to about 16 hoursunder a flowing argon atmosphere can be used effectively for thepreparation of a number of precursor materials. The precursor materialson removal from the furnace range from dark brown to black in color. Thecolor is dependent on the amount of carbon added in the initial reactionmixture.

FIG. 2 is a typical X-ray powder pattern obtained for a sample ofV—P—O/C precursor made at 700° for 4 hours. The powder pattern of thesematerials prepared at low temperature generally have a “featureless”powder pattern, which can be interpreted as being due to either thematerial being amorphous or that the obtained crystallites are verysmall nanoparticles.

EXAMPLE 2 Preparation of LiVPO₄F using VPO₄

LiVPO₄ was prepared according to the following reaction:LiF+VPO₄→LiVPO₄FThe LiF (2.6 g) and VPO₄ (1.46 g) were mixed and micronized. The amountof LiF added is dependent on the amount of residual carbon present inthe VPO₄. The stoichiometric amount of LiF is added based on the abovereaction. An allowance can be made for the amount of residual carbonleft over from the V—P—O/C synthesis. This is normally about 3 weightpercent. The mixture was then heated in the temperature range of about600° to about 700° C. for up to about 1 hour. At temperatures in excessof 700° C., it is believed that VF₃ sublimation occurs which leads tothe formation of Li₃V₂(PO₄)₃ (LVP-nasicon).

FIG. 3 shows an example of a powder pattern obtained for a sample ofLiVPO₄F. Refinement of the XRD data for the LiVPO₄F samples was carriedout using the Rietveld method. H. M. Rietveld, J. Appl. Crystallograph,2, (1969) 65. R. A. Young in “The Rietveld Method”, Chapter 1, OxfordScience Publications. A. C. Larsen and R. B. Von Dreele, Los AlamosLaboratory Report, NO-LA-U-86-746 (1987). The X-ray data can besatisfactorily refined using a structural model based on eitherTavorite, LiFePO₄OH (U.S. Pat. No. 6,387,568 Barker et al.) orAmblygonite, LiAlPO₄F (Groat et al, American Mineralogist, 88, 195(2003). The X-ray data for the LiVPO₄F samples derived from theoptimized synthesis conditions for this process favor the Amblygonitestructural model as the most likely structure of this model. (Suchoptimized conditions being V—P—O/C prepared at 700° C., followed byreaction with LiF at 700° C. to produce LiVPO₄).

FIG. 4 shows the fit obtained for the LiVPO₄F sample using the Rietveldanalysis. The refined cell parameters are given as space group P-1:a=5.16727(13) Å, b=5.30590(13) Å, c=7.28964(19) Å, α=108.9108(14)°,β=107.2137(13)°, γ=98.4002(16)° and cell volume=174.007(8) Å³; withfitting statistics being R_(wp) 11.08%, R_(p)=8.05% and x=2.352.

FIG. 5 shows a schematic representation (along the c axis) of theLiVPO₄F based on the Amblygonite structural model. The LiVPO₄F structurecomprises a three dimensional framework being built from [PO₄]tetrahedral and [VO₄F₂] octahedral with the oxygen atoms shared betweenthe PO₄ and VO₄F₂. This model predicts the presence of two distinctcrystallographic sites for alkali ions which explains theelectrochemical lithium extraction behavior exhibited by this material.

An electrode is made with 84% of the active material, 6% of Super Pconductive carbon, and 10% poly vinylidene difluoride. A cell with thatelectrode as cathode and lithium anode is constructed with anelectrolyte comprising 1 M LiPF₆ dissolved in 2:1 by weight mixture ofethylene carbonate:dimethyl carbonate.

FIG. 6 shows the first cycle constant current data obtained for the cellbuilt using the sample of LiVPO₄F. A slight inflection is seen in thedata during the charge process, which is related to preferentialdepopulation of one of the Li sites within the structure. No suchfeature is observed during the discharge process, indicating that duringreinsertion of the Li neither of the sites is preferred. Thisobservation is clearly supported by the observation of two peaks in thedifferential capacity plot obtained during EVS measurement. Long termcycling of this material shows good electrochemical properties.

EXAMPLE 3

An electrode active material comprising LiV_(1−x)Al_(x)PO₄F was madeaccording to the following reaction scheme:(1−x)VPO₄ +x AlPO₄+LiF →LiV_(1−x)Al_(x)PO₄F

The LiF, VPO₄ and AIPO₄ were mixed and micronized in the requiredamounts. If for example x=0.20.8 VPO₄+0.2 AlPO₄+LiF→LiVo_(0.8)Al_(0.2)PO₄FThen 1.167 g of VPO₄ were mixed with 0.244 g AlPO₄ and 0.259 g LiF. Themixture was then heated in the temperature range 600-700° C. for up to 1hour.

An electrode is made with 84% of the active material, 6% of Super Pconductive carbon, and 10% poly vinylidene difluoride. A cell with thatelectrode as cathode and a lithium anode is constructed with anelectrolyte comprising 1 M LiPF₆ dissolved in 2:1 by weight mixture ofethylene carbonate:dimethyl carbonate.

FIG. 7 shows the X-ray powder patterns for samples ofLiV_(1−x)Al_(x)PO₄F. The results shown in FIG. 7 show that high qualitysamples can be prepared relatively easily.

FIG. 8 is a plot of Al content versus unit cell volume, obtained fromRietveld analysis of several samples. The plot clearly shows a linearrelationship between Al content and the unit cell volume which isconsistent with Vegards law, i.e. formation of a solid solution seriesbetween the V and Al.

Varying the amount of Al in a sample makes it possible to vary theoperating voltage of the sample. FIG. 9 shows a comparison of theelectrochemical response of samples containing varying amounts of Al.Addition of more Al to a sample has the effect of reducing theovervoltage (i.e. voltage polarization) and is thought to be related tothe increase in substitutionial disorder of the material. The additionof Al on the V sites upsets the ordering (V-V-etc) of the transitionmetal. This will affect the resultant voltage characteristics to someextent. However, as Al is electrochemically inactive it has the effectof reducing the overall capacity of the material. Life cycling datasuggests that the Al doped samples have a lower fade rate then observedwith LiVPO₄F.

EXAMPLE 4

An electrode active material comprising Na_(1.2)VPO₄F_(1.2) was made asfollows. In a first step, a metal phosphate was made by carbothermalreduction of a metal oxide, here exemplified by vanadium pentoxide. Theoverall reaction scheme of the carbothermal reduction is as follows.0.5V₂O₅+NH₄H₂PO₄+C→VPO₄+NH₃+1.5H₂O+CO9.1 grams of V₂O₅, 11.5 grams of NH₄H₂PO₄ and 1.2 grams of carbon (10%excess) are used. The precursors were premixed using a mortar and pestleand then pelletized. The pellet was transferred to an oven equipped witha flowing argon atmosphere. The sample was heated at a ramp rate of 2°per minute to an ultimate temperature of 300° C. and maintained at thistemperature for three hours. The sample was cooled to room temperature,removed from the oven, recovered, re-mixed and repelletized. The pelletis transferred to a furnace with an argon atmosphere. The sample isheated at a ramp rate of 2° per minute to an ultimate temperature 750°C. and maintained at this temperature for 8 hours.

In a second step, the vanadium phosphate made in the first step wasreacted with an alkali metal halide, exemplified by sodium fluoride,according to the following reaction scheme.xNaF+VPO₄→Na_(x)VPO₄F_(x)14.6 grams of VPO₄ and 4.2 grams of NaF were used. The precursors arepre-mixed using a mortar and pestle and then pelletized. The pellet wastransferred to an oven equipped with a flowing argon atmosphere. Thesample was heated at a ramp rate of 2° per minute to an ultimatetemperature of 750° C. and maintained at this temperature for an hour.The sample was cooled and removed from the furnace.

To make Na_(1.2)VPO₄F_(1.2), the reaction is repeated with a 20% massexcess of sodium fluoride over the previous reaction. The precursorswere pre-mixed using a mortar and pestle and pelletized as before. Thesample was heated to an ultimate temperature of 700° C. and maintainedat this temperature for 15 minutes. The sample was cooled and removedfrom the oven. There is only a small weight loss during reaction,indicating almost full incorporation of the NaF. To make an activematerial of formula Na_(1.5)VPO₄F_(1.5) the reaction is repeated with anapproximate 50% mass excess of sodium fluoride over the first reaction.The sample is heated at 700° C. for 15 minutes, cooled, and removed fromthe oven.

An electrode is made with 84% of the active material, 6% of Super Pconductive carbon, and 10% poly vinylidene difluoride. A cell with thatelectrode as cathode and lithium foil as anode is constructed with anelectrolyte comprising 1 M LiPF₆ dissolved in 2:1 by weight mixture ofethylene carbonate:dimethyl carbonate.

EXAMPLE 5

An electrode active material comprising LiVP₂O₇ was made according tothe following reaction scheme.LiH₂PO₄+VPO₄→LiVP₂O₇+H₂OLiH₂PO₄ (10.39 g) and VPO₄ (14.59 g) were used. The precursors weremixed using a mortar and pestle and then pelletized. The pellet wastransferred to an oven equipped with a flowing argon atmosphere. Thesample was heated at a ramp rate of 2° per minute to an ultimatetemperature of 750° C. and maintained at this temperature for an hour.It has been found that this material can be prepared in temperaturesranging from about 650° C. to about 850° C. The sample is cooled andremoved from the furnace.

An electrode is made with 84% of the active material, 6% of Super Pconductive carbon, and 10% poly vinylidene difluoride. A cell with thatelectrode as cathode and carbon intercalation anode is constructed withan electrolyte comprising 1 M LiPF₆ dissolved in 2:1 by weight mixtureof ethylene carbonate:dimethyl carbonate.

FIG. 10 is a representative X-ray powder pattern for LiVP₂O₇. Thestructure of this material has been examined using the Rietveld methodusing the model presented by Rousse. Rousse et al., Int. J. Inorg. Mat.,3, 881 (2001). The obtained fit is presented in FIG. 11. The refinedunit cell lattice parameters are: a=4.8211(2) Å, b=8.1283(3) Å,c=6.9404(3) Å, α=90°, β=108.949(2)°, γ=90°, volume=257.24(2) Å³ withR_(wp)=12.97%, R_(p)=9.23% and x²=1.30.

The structure of LiVP₂O₇ can be described as a 3-D framework of cornersharing VO₆ octahedra and P₂O₇ groups. This framework arrangementprovides tunnels in which Li ions are coordinated tetrahedrally, asshown in FIG. 12.

Previous studies by Uebou and Wurm have shown that this material hasrelatively poor electrochemical properties, with discharge capacities inthe region of 50 mAh/g observed at a very low rate (typically a very lowrate). Uebou et al., Solid State Ionics, 148, 323, (2002). Wurm et al.,Chem. Mater., 14, 2701, (2002). The present inventors have found that byproducing a composite of this diphosphate and a high surface areacarbon, there is a noticeable improvement in the electrochemicalproperties. The properties are shown in FIG. 13.

The data in FIG. 13 shows a discharge capacity in the region of about 68MAh/g. Taking into account the residual carbon this discharge capacityhas a value closer to about 71 mAh/g. Although this would appear to beonly a modest improvement over that reported by Uebou and Wum, theseexperiments were performed at a rate in the region of C/15. It isbelieved that some of the irreversibility is due to the upper voltagelimit used in this experiment.

FIG. 14 shows the results of an EVS experiment performed using voltagelimits of 2.5 to 4.7 volts (versus Li). The reversible specific capacityfor LiVP₂O₇ is 93 mAh/g. It was noted however, that the capacityincreased slowly over the first ten cycles, reaching 101 mAh/g after thetenth cycle. Examination of the differential capacity versus cellvoltage plot shows that this system works with relatively lowpolarization. The differential capacity plot shows some evidence ofdecomposition at voltages greater than approximately 4.35 volts.

Similarly, good results have been obtained in Li ion cells, with EVSresults after 10 cycles shown in FIG. 15. It can be seen therefrom thatthere is a decrease in observed cell polarization. FIG. 16 shows theresults of life cycle experiments performed with this material.

EXAMPLE 6

An electrode active material comprising Li_(0.1)Na_(0.9)VPO₄F was madeaccording to the following reaction scheme.xLiF+(1−x)NaF+VPO₄→Li_(x)Na_(1−x)VPO₄FAs an alternative to using alkali fluorides, a reaction between VPO₄ andNH₄F and a mixture of Li₂CO₃ and Na₂CO₃ may also be used.

To make Li_(0.1)Na_(0.9)VPO₄F, 1.459 grams VPO₄, 0.026 grams of LiF, and0.378 grams of NaF were premixed, pelletized, placed in an oven andheated to an ultimate temperature of 700° C. The temperature ismaintained for fifty minutes after which the sample is cooled to roomtemperature and removed from the oven. To make Li_(0.95)Na_(0.05)VPO₄F,1.459 grams of VPO₄, 0.246 grams of LiF, and 0.021 grams of NaF aremixed together and heated in an oven as in the previous step. Anelectrode is made with 84% of the active material, 6% of Super Pconductive carbon, and 10% poly vinylidene difluoride. A cell with thatelectrode as cathode and carbon intercalation anode is constructed withan electrolyte comprising 1 M LiPF₆ dissolved in 2:1 by weight mixtureof ethylene carbonate:dimethyl carbonate.

EXAMPLE 7

An electrode active material comprising NaVPO₄F is made hydrothermallyaccording to the following reaction scheme.NaF+VPO₄→NaVPO₄F1.49 grams of VPO₄ and 1.42 grams of NaF are premixed with approximately20 milliliters of deionized water, transferred and sealed in a ParrModel 4744 acid digestion bomb, which is a Teflon lined stainless steelhydrothermal reaction vessel. The bomb is placed in an oven and heatedat a ramp rate of 5° per minute to an ultimate temperature of 250° C. tocreate an internal pressure and maintained at this temperature forforty-eight hours. The sample is slowly cooled to room temperature andremoved from the furnace for analysis. The product sample is washedrepeatedly with deionized water to remove unreacted impurities. Then thesample is dried in an oven equipped with argon gas flow at 250° C. forone hour. An electrode is made with 84% of the active material, 6% ofSuper P conductive carbon, and 10% poly vinylidene difluoride. A cellwith that electrode as cathode and carbon intercalation anode isconstructed with an electrolyte comprising 1 M LiPF₆ dissolved in 2:1 byweight mixture of ethylene carbonate:dimethyl carbonate.

EXAMPLE 8

An electrode active material of formula NaVPO₄OH is made according tothe following reaction scheme.NaOH+VPO₄→NaVPO₄OH

In this Example, the reaction of the Example 7 is repeated, except thatan appropriate molar amount of sodium hydroxide is used instead ofsodium fluoride. The reaction is carried out hydrothermally as inExample 7. The hydroxyl group is incorporated into the active materialat the relatively low temperature of reaction. An electrode is made with84% of the active material, 6% of Super P conductive carbon, and 10%poly vinylidene difluoride. A cell with that electrode as cathode andcarbon intercalation anode is constructed with an electrolyte comprising1 M LiPF₆ dissolved in 2:1 by weight mixture of ethylenecarbonate:dimethyl carbonate.

EXAMPLE 9

An electrode active material comprising NaVPO₄F is made according to thefollowing reaction scheme.0.5Na₂CO₃+NH₄F+VPO₄→NaVPO₄F+NH₃+0.5CO₂+0.5H₂O

1.23 grams of VPO₄, 0.31 grams of NH₄F, and 0.45 grams Na₂CO₃ arepremixed with approximately 20 milliliters of deionized water andtransferred and sealed in a Parr Model 4744 acid digestion bomb, whichis a Teflon lined stainless steel reaction vessel. The bomb is placed inan oven and heated to an ultimate temperature of 250° C. and maintainedat this temperature for forty-eight hours. The sample is cooled to roomtemperature and removed for analysis. The sample is washed repeatedlywith the deionized water to remove unreacted impurities and thereafteris dried in an argon atmosphere at 250° C. for an hour. An electrode ismade with 84% of the active material, 6% of Super P conductive carbon,and 10% poly vinylidene difluoride. A cell with that electrode ascathode and carbon intercalation anode is constructed with anelectrolyte comprising 1 M LiPF₆ dissolved in 2:1 by weight mixture ofethylene carbonate:dimethyl carbonate.

EXAMPLE 10

Electrode active materials comprising compounds of the formulaLiV_(1−x)Al_(x)PO₄ were made according to the following reaction scheme:(1−x) VPO₄+x AlPO₄+LiH₂PO₄→LiV_(1−x)Al_(x)P₂O₇+H₂O

The precursors were mixed using a mortar and pestle and then palletized.The pellet was transferred to an oven equipped with a flowing argonatmosphere. The samples were heated at a ramp rate of 2° per minute toan ultimate temperature of about 650° C. to about 850° C. and maintainedat these temperatures for about 4 to about 8 hours. The sample is cooledand removed from the furnace. An electrode is made with 84% of theactive material, 6% of Super P conductive carbon, and 10% polyvinylidenedifluoride. A cell with that electrode as cathode and lithium anode isconstructed with an electrolyte comprising 1M LiPF₆ dissolved in 2:1 byweight ethylene carbonate to dimethyl carbonate is constructed andtested.

Al³⁺ is electrochemically inactive and therefore reduces the amount ofLi that can be extracted. Thus many of the samples prepared were lowerAl content samples, typically in the range of 5-15% Al doping. The X-raypatterns for a selection of samples so prepared are shown in FIG. 17.

The electrochemical properties of the samples so prepared are shown inFIG. 18.

EXAMPLE 11

An electrode active material comprising Li₃V₂(PO₄)₃ was made accordingto the following reaction scheme.Li₃PO₄+2VPO₄→Li₃V₂(PO₄)₃LiPO₄ (11.58 g) and VPO₄ (29.18 g) were used. The precursors were mixedusing a mortar and pestle and then pelletized. The pellet wastransferred to an oven equipped with a flowing argon atmosphere. Thesamples were heated at a ramp rate of 2° per minute to an ultimatetemperature of about 650° C. to about 850° C. and preferably 700 to 750°C. and maintained at these temperatures for about 1 to about 8 hours.The sample is cooled and removed from the furnace.

FIG. 19 shows a representative X-ray pattern of a sample prepared asabove.

An electrode is made with 84% of the active material, 6% of Super Pconductive carbon, and 10% poly vinylidene difluoride. A cell with thatelectrode as cathode and a lithium anode is constructed with anelectrolyte comprising 1 M LiPF₆ dissolved in 2:1 by weight mixture ofethylene carbonate:dimethyl carbonate.

FIG. 20 shows the electrochemical properties of the sample.

EXAMPLE 12

An electrode active material comprising Na₃V₂(PO₄)₂F₃ is made asfollows. First, a VPO₄ precursor is made according to the followingreaction scheme.V₂O₅+2 (NH₄)₂HPO₄+2 C→2 VPO₄+4 NH₃+3 H₂O+2 COA mixture of 18.2 g (0.1 mol) of V₂O₅, 26.4 g (0.2 mol) of (NH₄)₂HPO₄,and 2.64 g (0.2 mol+10% mass excess) of elemental carbon was made, usinga mortar and pestle. The mixture was pelletized, and transferred to abox oven equipped with an argon gas flow. The mixture was heated to atemperature of about 350° C., and maintained at this temperature for 3hours. The mixture was then heated to a temperature of about 750° C.,and maintained at this temperature for 8 hours. The product is thencooled to ambient temperature (about 21° C.).

Na₃V₂(PO₄)₂F₃ was then made from the VPO₄ precursor. The material wasmade according to the following reaction scheme.2 VPO₄+3 NaF→Na₃V₂(PO₄)₂F₃A mixture of VPO₄ (2.918 g) and NaF (1.26 g) was made, using a mortarand pestle. The mixture was pelletized, and transferred to atemperature-controlled tube furnace equipped with an argon gas flow. Themixture is heated at a ramp rate of about 2°/minute to an ultimatetemperature of about 750° C. for 1 hour Temperatures can be in theregion of 700-800° C. for these samples and can be heated in this regionfor about one to about four hours. The product is then cooled to ambienttemperature (about 20° C.). A representative X-ray powder pattern isshown in FIG. 21 X-ray powder diffraction analysis for the Na₃V₂(PO₄)₂F₃material indicated the material to be single phase with a tetragonalstructure (space group P42/mnm). The unit cell parameters (a=9.0304(5)Å, c=10.6891(9) Å) were calculated from a least squares refinementprocedure, in fair agreement with the structural analysis forNa₃V₂(PO₄)₂F₃ described by Meins et al., J. Solid State Chem., 148, 260,(1999). (i.e. a=9.047(2) Å, c=10.705(2) Å).

EXAMPLE 13

0.5 V₂O₅+(NH₄)₂HPO₄+C→VPO₄+NH₃+1.5 H₂O+CO

Vanadium oxide (V₂O₅; 9.10 g), diammonium hydrogen phosphate (13.2 g)and elemental carbon (1.32 g, 10% mass excess) were weighed and pouredinto a micronising pot. The materials were then micronised for 15minutes. This process step has the dual purpose of providing intimatemixing and dispersion of the raw materials to produce a homogenousmixture and reducing particles size of the material due to thegrinding/milling action. After micronising, the resulting powder waspressed to form a pellet. The pellet was placed in a crucible and placedin a tube furnace. The pellet was fired at 700° C. at a ramp rate of 2°C./minute with a 16 hour dwell under an inert atmosphere. After firing,the pellet was broken up and ground to produce a powder. FIG. 23 showsthe X-rd trace for the resulting VPO₄. The trace shows that the VPO₄ isan amorphous V—P—O/C precursor.VPO₄+LiF→LiVPO₄F

The VPO₄ (1.46 g) precursor so obtained was then micronised for 15minutes with LiF (0.26 g). After micronising, the resultant powder waspressed to form a pellet was placed in a crucible, sealed by a secondcrucible and placed in a tube furnace. The pellet is fired at 700° C. ata ramp rate of 2° C./minute with a one hour dwell under an inertatmosphere. After firing, the pellet was broken up and ground to producethe final LiVPO₄F material. FIG. 24 shows the Xrd trace for theresulting LiVPO₄F.

The examples and other embodiments described herein are exemplary andnot intended to be limiting in describing the full scope of compositionsand methods of this invention. Equivalent changes, modifications andvariations of specific embodiments, materials, compositions and methodsmay be made within the scope of the present invention, withsubstantially similar results.

1. A method for making a vanadium phosphate precursor comprising mixingV₂O₅ with a phosphate compound and a carbon containing compound or acarbon precursor to form a mixture, and heating the mixture at atemperature and for a time sufficient to form a precursor selected fromthe group consisting of amorphous V—P—O/C precursor and nanocrystallineVPO₄ precursor.
 2. The method according to claim 1 wherein the phosphatecompound is (NH₄)₂HPO₄ or (NH₄)H₂PO₄.
 3. The method according to claim 1wherein the carbon is a conductive high surface area carbon with asurface area of from about 1 to about 1000 m²/g.
 4. The method accordingto claim 3 wherein the carbon is selected from carbon black; Super P,Shawinaghan black and mixtures thereof.
 5. The method according to claim2 wherein the carbon is selected from a graphitic carbon and organicprecursor materials.
 6. The method according to claim 1 wherein themixture is heated at a temperature in the range from about 650° C. toabout 900° C.
 7. The method according to claim 3 wherein the temperatureis from about 700° C. to about 800° C.
 8. A method for making a vanadiumphosphate compound of the formula:A_(a)V_(1−x)M_(x)(PO₄)_(d)Z_(f).  (I)wherein A is selected from thegroup consisting of Li, Na, K and mixtures thereof; a is greater than0.1 and less than or equal to 3; x is greater than or equal to zero andless than 1; d is greater than 0 and less than or equal to 3; M is ametal selected from the group consisting of Al, Ti, Cr, Fe, Mn, Mo, andNb; Z is F, Cl, or OH: and f is greater than or equal to zero but lessthan or equal to three; comprising mixing the VPO₄ precursor or V—P—O/Cprecursor produced according to the method of claim 1 with an alkalimetal containing compound to form a mixture and heating the mixture at atemperature and for a time sufficient to form the vanadium phosphatecompound.
 9. The method according to claim 7 wherein the mixture furthercomprises a second metal containing compound.
 10. The method accordingto claim 7 wherein the alkali metal compound is selected from the groupconsisting of LiF, NaF, NaOH, LiOH, Na₂CO₃ and Li₃PO₄.
 11. The methodaccording to claim 8 wherein the metal containing compound comprises ametal ion of a metal selected from the group consisting of Al, Ti, Cr,Fe, Mn, Mo and Nb.
 12. The method according to claim 7 wherein thevanadium phosphate compound produced is selected from LiVPO₄,LiV_(1−x)Al_(x)PO₄F, Na_(x)VPO₄F_(x), Li_(0.1)Na_(0.9)VPO₄F, NaVPO₄F,NaVPO₄OH, NaVPO₄F, Li₃V₂(PO₄)₃, LiV_(0.75)Al_(0.25)PO₄F,LiV_(0.5)Al_(0.5)PO₄F, Na_(1.2)VPO₄F_(1.2) and Na₃V₂(PO₄)₂F₃.
 13. Amethod for making a vanadium phosphate compound of the formula:A_(a)V_(1−x)M_(x)P₂O₇  (I)wherein A is selected from the groupconsisting of Li, Na, K and mixtures thereof; a is greater than 0.1 andless than or equal to 3; x is greater than or equal to zero and lessthan 1; and M is a metal selected from the group consisting of Al, Ti,Cr, Fe, Mn, Mo and Nb; comprising mixing the VPO₄ precursor or V—P—O/Cprecursor produced according to the method of claim 1 with an alkalimetal containing compound to form a mixture and heating the mixture at atemperature and for a time sufficient to form the vanadium phosphatecompound.
 14. The method according to claim 7 wherein the mixturefurther comprises a second metal containing compound.
 15. The methodaccording to claim 7 wherein the alkali metal compound is selected fromthe group consisting of LiF, NaF, NaOH, LiOH, Na₂CO₃ and Li₃PO₄.
 16. Themethod according to claim 8 wherein the metal containing compoundcomprises a metal ion of a metal selected from the group consisting ofAl, Ti, Cr, Fe, Mn, Mo and Nb.
 17. The method according to claim 7wherein the vanadium phosphate compound produced is LiVP₂O₇.
 18. Amethod for making a vanadium phosphate precursor comprising mixing V₂O₅with a phosphate compound and heating the mixture in a reducingatmosphere at a temperature and for a time sufficient to form aprecursor selected from the group consisting of amorphous V—P—O/Cprecursor and nanocrystalline VPO₄ precursor.
 19. The method accordingto claim 18 wherein the phosphate compound is (NH₄)₂HPO₄ or (NH₄)H₂PO₄.20. The method according to claim 18 wherein the mixture additionallycomprises a conductive high surface area carbon with a surface area offrom about 1 to about 1000 m²/g.
 21. The method according to claim 20wherein the mixture additionally comprises carbon selected from carbonblack; Super P, Shawinaghan black and mixtures thereof.
 22. The methodaccording to claim 18 wherein the mixture additionally comprises carbonselected from a graphitic carbon and organic precursor materials. 23.The method according to claim 18 wherein the mixture is heated at atemperature in the range from about 650° C. to about 900° C.
 24. Themethod according to claim 18 wherein the temperature is from about 700°C. to about 800° C.